Project Summary/Abstract Childhood growth and development involves significant changes to many tissues in the body, including connective soft tissues in the musculoskeletal system, such as tendons and ligaments. While these soft tissue changes are needed to adapt to major changes in anatomy and biomechanics during the transition from early childhood to late adolescence, they can complicate clinical interventions in the case of pathologies such as neuromuscular disorders or orthopedic injuries. In the instance of cerebral palsy (CP), a common neuromuscular disorder often resulting in altered posture and gait, clinical treatments such as osteotomies, muscle-tendon lengthening procedures, and tendon-transfers must be designed to accommodate ongoing growth-related changes in tissue geometry and stiffness. While there are current methods for assessing geometric changes in tissues during growth, we lack a non-invasive means of directly measuring the stiffness of tendons in individuals, such as those in these pediatric populations. As such, the objective of this project is two-fold: to develop and validate a novel, non-invasive tool and a computational model for measuring tendon stiffness in the lab, and to use this non-invasive tool to characterize age-related changes in tendon stiffness in a pediatric cohort. Specifically, Aim 1 of this proposal describes the combined use of two unique methods previously developed in this laboratory to non-invasively assess regional tendon stiffness. This tool will combine a cine ultrasonic measurement of regional tissue strain and the measurement of shear wave propagation through the tendon, which can be used to determine tensile tissue stress. Parameters from this testing will be used to drive and validate a finite element model of individualized tendon biomechanics. Then, in Aim 2, non-invasive techniques such as those described in Aim 1 will be applied to measure changes in the stiffness of the Achilles tendon in pediatric and adolescent subjects. Successful completion of these aims will result in the validation of a novel, non-invasive method for measuring in vivo tendon stiffness in young subjects, and will contribute to an enhanced understanding of the timing of age- and sex-specific changes in tendon stiffness during childhood and adolescent growth. These outcomes have the potential to improve predictions from clinical procedures in pediatric populations suffering from musculoskeletal disorders such as CP and surgical reconstructions for orthopedic injuries such as ligament and tendon ruptures. In addition, the technical and professional development described in this training plan will prepare the PI for a successful career in educating STEM students while performing research in the field of biomechanics with applications in pediatric clinical populations.